Nonlinear steady-state vibration analysis of rotor by substructure synthesis

A new nonlinear steady-state calculation by substructure synthesis is presented for large-order rotordynamic systems with a few nonlinear elements, which is considered popular in actual rotating machines. In this paper, linear dynamic and static structural relations are reduced to small degrees of freedom on nonlinear elements such as nonlinear bearings. Using discreet Fourier transform (DFT, also using FFT), and the Newton-Raphson method, harmonic balance for this reduced nonlinear system can be obtained as efficiently as for a simple rotor system. As examples, the effect of a friction damper on a turbine blade model and nonlinear unbalance response of an actual turbine rotor supported by squeeze film dampers without centering springs are discussed.